Tints Flashcards
Why do we dispense tints?
- To provide protection from ultraviolet light-
- To provide protection from glare (disability and
discomfort) - glare is any light causes discomfort- which causes watery eyes - To provide visual comfort
- Therapeutic and medical
- Contrast filters- increasing contrast of objects so can see clearer for e.g in a sport like a football use a green tint etc.
Who can benefit from a tint?
-a patient that could have early signs of cataract- which elevate their discomfort.
What do tints protect against?
certain wavelengths of light such as infrared- which can be damaging to the eye.
Why do we need protection from the different wavelengths of light - UVA ?
linked to cataracts and retinal damage - deeply penetrating
Why do we need protection from UVB?
linked to cataracts1 and photokeratitis
Why do we need protection from the visible spectrum ?
can cause disability and discomfort glare
Why do we need protection from Infrared ?
800+nm causes heat cataract and retinal/choroidal burns
Do all sunglasses have UV protection ?
No
-UV is a seperate clear coating and you can then go onto adding a tint to it as it is not always provided.
Why are we more concerned about UV coating a tinted lens?
-pupil size increase due to dark tint and more light is let into the eye- change the ocular dynamics of the eye
What can the amount of light entering the eye be altered by ?
- absorption
- reflection
What are mirror coatings supplied with?
Supplied with a dark tint to prevent the wearer seeing themselves in the mirror coating.
What do mirror coatings do?
- they have Tint depth which also influences the amount of reflection
- they Don’t wear well- can easily be scratched affecting them
What do the mirror coatings protect from?
-Protection from absorption and reflection
How can you describe the tint?
- State the tint by colour
- Depth in percentage
- Light transmission factor (LTF) - FOR how light or dark you want the tint to be so by telling how much light you want transmitted through from this factor
- Absorbance (ABS) - to tell how much light is absorbed by the lens
Is an 85% LTF lens light or dark?
light lens - letting 85% of light through
What is the equivalent ABS?
15%
What colour tint does a patient choose?
-To enhance contrast? Drivewear Sports tints -Personal preference? -Cosmesis? Frame choice -Protection Certain colours provide protection
What is the colour of the tint for?
the light that is letting through the lens
What does a transmission chart do and tell you?
uses spectral anomaloscope which plots the transmittance of radiation at each wavelength
Why is a N tint good?
- filter out all wavelengths roughly the same they don’t distort colours much whereas a contrasting tint will.
- So when a patient sees through them there is no distortion
What is a N tint?
a neutral tint which is grey
Who is a N tint good for ?
drivers- don’t want traffic light colours being distorted
-Architectures
What tints are available?
- Fixed
- Graduated
- Photochromic
- Polarised
What are fixed tints ?
- Same colour throughout the lens
- tint absorbs 1mm into the material - just front surfaces
What are the methods of tinting fixed tints?
- Plastic- dip dying
- Glass- solid or laminated
How do we tint the fixed tints in a glass material? (2 ways)
- Solid - the tint is introduced tot he lens when it’s molten- a tint is solid throughout the material/ lens
- if want green tint - iron added to the molten mix
- Laminate the lens- a laminated tint is a thin sheet which is laminated or vacuum coated onto one surface of the lens- a tint is only one surface of the lens.
What do we do when deciding between a solid and laminated tint?
Lamberts Law - thinking about the absorption of the material is proportional to its thickness - which means the thicker material the darker the tint
- If have patient which is -8 = laminated is better-
- plano lens- better to have solid.
What is a solid tint?
dispersed in the whole lens/material
What is a laminated / equitent tint?
only at one surface of the lens.
-not affected by tint at all - equal across the lens
What is a graduated tint ?
Can be single or dual coloured.
- They are darker at top graduating to a lighter colour at the bottom.
- Change in gradient
Why is the top darker and the bottom lighter in a graduated tint an advantage?
better for an elderly patient who needs reading glasses
What is a photochromic tint?
- Darken due to the energy provided by UV.- use energy to alter the structure- when hit UV light turns dark
- Darken quicker than they return back to light - on a sunny day will turn dark MORE and less UV means less dark.
- No separate sunglasses required
- Tint variable
- Temperature dependent- work better in cold environments than hot
- Full UV400 protection - if remove this will limit how it works - not as well
- Less reactive behind a UV filter- e.g. car windscreen.
What benefits and advice do you think you should give your patients regarding
Darken quicker than they return back to light
- tell patient first so they know that when going from inside to outside the darken quickly whereas going from out to in they take longer to turn colour.
- explain to the patient as they might think it’s faulty
- might be a health and safety hazard - if walking straight in - wont be able to see so suddenly.
- care when walking into buildings
No separate sunglasses required
- save money
- conviencince - no swapping glasses
Tint variable
comfort at all light variables
Less reactive behind a UV filter- e.g. car windscreen
- get glare - better outside the car
Less reactive behind a UV filter- e.g. car windscreen
- better outside the car
- may not get as dark when driving
Residual colour with age
- older styles they get old after time (get yellow tint after a while ) - may affect vision in darker conditions.
What can photochromatic lenses be made in ?
-Glass- which contain
Silver halides- separate when activated by UV - when separated they go darker and recombine and get lighter
Equi-tint can be used on high prescriptions
-Plastic- use
Pyrans and oxazines in the 100-150 microns of the front
the surface of the lens
Molecules rotate on activation by UV- don’t split and as they rotate they become darker
Why Polarised lenses?
- Unpolarised light- light which vibrates in all directions
- Polarised light- it maintains in the one direction- which can cause glare and mirror effect
- Brewster angle- if angle between the refracted and reflected beam is 90° then the reflected beam will be completely plane polarised.
Why is polarised light not good?
can cause glare and mirror effect e.g when driving
What is polarized light?
polarized in the plane parallel to the
reflecting surface
e.g surface of water
How can we polarise lenses?
- Axis of the filter set vertical
- BS tolerance 5 degrees
-Stretched iodine crystals
-darker tint more polarisation occurring
-
How can we tell our patient is wearing a polarised lens?
- do that by thinking about the effect of holding up another polarised lens in front of them
- if you have 2 polarised lens - it will let some light through - the picture will be less clear- contract reduced by still able to see the image
- if by rotating the filters at right angles to one another - block both vertical and horizontal meridian- won’t see a image
What are IR lenses?
- need to use with glass lens
- Exposure from sun, furnaces and with explosions!
- Linked to heat cataract, retinal and choroidal lesions
- Cant protect with CR39
- Rayban G-15- ferrous oxide- green tint - glass lens
UV light exposure ?
-Should protect eyes all year round not just in summer or winter.
UV damage to the eye can be reversed?
No
Do you need to wear sunglasses on a cloudy day
Yes
Are children more vulnerable to UV ?
Yes
Do darker tinted lenses provide more UV protection?
No
Do all sunglasses offer UV protection?
No
Are your eyes more sensitive to UV than your skin?
Yes
IS UV levels are higher in tropical areas?
Yes
